Method and apparatus particularly useful for treating osteoporosis

ABSTRACT

A method and apparatus for increasing the density and strength of bone, particularly for preventing or treating osteoporosis, by subjecting the bone to unfocussed compressional shock waves.

The present invention relates to a method and apparatus particularlyuseful for treating osteoporosis.

Osteoporosis is a bone disorder which affects middle and old age people,especially women. It is characterized by an abnormal loss of bonetissue, and consequently by a decrease in the density of the bone. Thereduction in bone density reduces the strength of the bone such as tomake the afflicted person susceptible to easy fracture, particularly ofthe pelvis (hip), spine, femoral neck, and forearm.

Osteoporosis affects millions of elderly people. In the USA, it affectsabout one out of every four women over the age of 45, and half of allwomen over the age of 60. Each year approximately 200,000 persons breaka hip because of osteoporosis. It is therefore one of the major causesfor prolonged hospitalization of the elderly; and resultingcomplications, particularly from hip fracture, constitute a frequentcause of death in the USA.

At the present time there is no generally accepted cure forosteoporosis, although various treatments are used with varying degreesof success. Thus, calcium supplementation, regular exercise, andenhanced physical activity may prevent deterioration of the bone; and ata later stage, more elaborate treatment, such as the administering ofhormones, calcium, phosphate and vitamin D analogues may be used.

An object of the present invention is to provide a novel method ofincreasing the density and strength of the bone, particularly forpreventing or treating osteoporosis. Another object of the invention isto provide apparatus for use in such treatment.

According to one aspect of the present invention, there is provided amethod of increasing the density and strength of the bone, particularlyfor preventing or treating osteoporosis comprising subjecting the boneto unfocussed compressional shock waves. Such unfocussed shock wavesthus produce dynamic repetitive loading of the bone. This increases themean bone density, and thereby strengthens the bone against fracture.

According to further features in the preferred embodiments of theinvention described below, the unfocussed shock waves are applied to thebone at an intensity of 50-500 atmospheres, and in the form ofsubstantially planar, unfocussed wavefronts covering an area of from 10to 150 cm² of the bone.

According to one described embodiment, the unfocussed shock waves areapplied by a point-source shock wave generator located at the focalpoint of a paraboloidal reflector which reflects the shock waves to forma substantially planar, unfocussed wavefront. More particularly, in thedescribed preferred embodiment the shock waves are generated by a sparkgap, preferably an electrical spark gap.

A second embodiment is described wherein the shock waves are generatedby an area-source shock wave generator, particularly an electromagneticdevice.

Generally speaking, the shock waves may be generated by the same typesof shock wave generators as are used in lithotripters, namely devicesdesigned to fragment upper urinary tract stones, gallstones, etc., byfocussing shock waves on the stones. The shock waves may be ofsubstantially the same duration and rate as in lithotripters, exceptthat instead of applying shock waves in a focussed condition, in thepresent invention the shock waves are applied in an unfocussed conditionso as to repetitively and dynamically load a substantial area of thebone being treated.

The invention also provides apparatus for increasing the density andstrength of the bone, particularly for preventing or treatingosteoporosis, in accordance with the above method.

Further features and advantages of the invention will be apparent fromthe description below.

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 diagrammatically illustrates one form of apparatus constructed inaccordance with the present invention;

FIG. 2 is an enlarged view of the main parts of the apparatus of FIG. 1involved in the treatment of bone in accordance with the presentinvention; and

FIG. 3 is a view similar to that of FIG. 2 but illustrating a variationsin the apparatus.

The apparatus illustrated in FIG. 1, and therein designated 2, maybasically be a known lithotripter apparatus used for fragmenting stones,e.g., kidney stones, except that the shock waves produced are in anunfocussed condition rather than in a focussed condition as in alithotripter. In addition, the apparatus 2 is preferably mounted onwheels 4 to make it mobile and thereby to facilitate its application toany desired bone of a patient 6, such as the pelvis or femur exhibitingosteoporosis. The treatment is effected by a shock wave generator,generally designated 8, projecting from one side of the apparatus 2 andadapted to be coupled to the bone being treated by an acousticalcoupling 10. The unfocussed shock waves are applied via the acousticcoupler 10 as substantially planar, unfocussed wavefronts covering arelatively large area of the bone being treated, e.g., an area of from10 to 150 cm².

The manner of generating and applying the unfocussed shock waves is moreparticularly illustrated in FIG. 2. Thus, the unfocussed shock wavegenerator 8 is shown as including a spark gap 12 at the focal point of aparaboloidal reflector 14. Such a reflector, when the shock wavegenerator is located at its focal point, reflects the shock waves in a"collimated" (unfocussed) form to produce a substantial planar,unfocussed wavefront. Reflector 14 thus reflects the shock waves to forma substantially planar, unfocussed wavefront, which are propagatedthrough the acoustical coupler 10, as indicated by lines 16.

The construction illustrated in FIG. 2, including a paraboloidalreflector 14 with the spark gap 12 located at its focal point, it is tobe clearly distinguishes from a conventional lithotripter producing afocussed shock wave. Thus, the conventional lithotripter uses anellipsoidal reflector with the shock wave generator located at one focalpoint thereof, so that the generated shock waves are focussed at thesecond focal point of the ellipsoidal reflector where the kidney stone,or other object to be fragmented, is located.

The acoustical coupler 10, through which the generated shock waves arecoupled to the patient, may also be of the type used in lithotripters.Thus, the acoustic coupler 10 includes a flexible envelope 18 containinga coupling liquid 20, such as water. A suitable acoustic gel may beprovided where the envelope contacts the patient to effect good acousticcoupling to the patient.

As shown in FIG. 2, the acoustic coupler 10 directly contacts the flesh22 of the patient. The patient's flesh has substantially the samedensity as the water 20 (or other liquid) used in the acoustic coupler10, so that the generated unfocussed shock wave propagates through it insubstantially the same form as through the acoustic coupler 10. The bone24 of the subject, however, is of a substantially different density fromthat of either the flesh 22 or the liquid 20 in the acoustic coupler 10,and therefore the unfocussed shock waves apply a compressional forceagainst the bone 24.

It will thus be seen that the repetitve application of the unfocussedshock waves to the patient's skin will subject the bone 24 to dynamicrepetitive loads. Such loads increase the mean bone density of the bone24, and thereby strengthen the treated bone against the possibility offracture.

In the apparatus illustrated in FIGS. 1 and 2, the shock wave generator8 is of the spark gap type. It is supplied by a high voltage generator26 including a capacitor 28 (or bank of capacitors) charged by a highvoltage source 30 and periodically discharged by a switch 32 to applythe high voltage to the spark plug 12 in the shock wave generator 8.

The apparatus illustrated in FIG. 1 further includes a control panel,schematically indicated by box 34, and a water system, schematicallyillustrated by box 36, for supplying water to the acoustic coupler 10.

Instead of using a point-source type shock wave generator for generatingthe unfocussed shock waves as illustrated in FIGS. 1 and 2, there mayalso be used an area-source type shock wave generator, such as one thatincludes an electromagnetic device for generating the shock waves.Examples of such electromagnetic-type shock wave generators aredescribed in U.S. Pat. Nos. 4,674,505, 4,796,608 and 4,782,821. Such anelectromagnetic-type shock wave generator is schematically illustratedin FIG. 3.

Thus, as shown in FIG. 3, the shock wave generator, therein designed108, includes an electromagnetic device 112, such as a flat pancakecoil, which is energized by a bank of capacitors 128 charged by a highvoltage source 130 and periodically discharged through theelectromagnetic device 112 by the closing of an electrical switch 132.The apparatus illustrated in FIG. 3 also includes an acoustical coupler110 for propagating the generated shock waves in an unfocussed conditionvia the patient's flesh 122 to the patient's bone 124, in the samemanner as described above with respect to FIGS. 1 and 2.

Other types of shock wave generators, as used in lithotripter devices,may also be used in the present method, except of course the generatedshock waves are applied in an unfocussed condition to the bone, ratherthan in a focussed condition. For example, the shock wave generatorcould also be of the piezoelectric crystal type, as described forexample in U.S. Pat. No. 4,617,931. Generally speaking, except for thefact that the shock waves are applied in an unfocussed condition, ratherthan in a focussed condition as in the conventional lithotripters, theshock waves may be generated and applied for the same durations and atthe same frequencies as in the conventional lithotripters.

The unfocussed shock waves preferably are applied over a relativelylarge surface of the bone to be treated, for example to cover an area offrom 10 to 150 cm². The intensity of the shock waves may be from 50-500atmospheres. Each shock wave is of a duration of a few microseconds, asin a conventional lithotripter, and is preferably applied at a frequencyof 1-10 shock waves per second, for a period of 5-30 minutes in eachtreatment. The number of treatments depends on the particular patient.Such a treatment as described above subjects the bone to dynamicrepetitive loads, and thereby strengthens the bone by increasing itsmean density.

While the invention has been described with respect to two preferredembodiments, it will be appreciated that these are set forth merely forpurposes of example, and that many other variations, modifications andapplications of the invention may be made.

What is claimed is:
 1. A method of increasing the density and strength of bone, comprising subjecting said bone to substantially planar, collimated compressional shock waves having a substantially constant intensity as a function of distance from a shock wave source, and wherein said collimated shock waves are applied to the bone at an intensity of 50-500 atmospheres.
 2. The method according to claim 1, wherein said collimated shock waves are applied in the form of a substantially planar, collimated wavefront covering an area of from 10 to 150 cm² of the treated bone.
 3. The method according to claim 1, wherein said collimated shock waves are applied by a point-source shock wave generator located at the focal point of a paraboloidal reflector which reflects the shock waves to form a substantially planar, collimated wavefront.
 4. The method according to claim 3, wherein the collimated shock waves are propagated from the reflector to the bone via a liquid compressional-wave acoustic coupler.
 5. The method according to claim 3, wherein said shock waves are generated at said focal point of the paraboloidal reflector by a spark gap.
 6. The method according to claim 1, wherein said collimated shock waves are generated by an area-source shock wave generator.
 7. The method according to claim 1, wherein said collimated shock waves are applied to bone at a rate of 1-10 shock waves per second.
 8. The method according to claim 1, wherein said collimated shock waves are applied to the bone for periods of 5-30 minutes each.
 9. Apparatus for increasing the density and strength of bone, comprising: a shock wave generator for generating compressional shock waves, including a collimator for applying the generated shock waves in a substantially planar, collimated condition to the bone, said shock waves having a substantially constant intensity as a function of distance from said shock wave generator, andwherein said shock wave generator generates shock waves of an intensity of 50-500 atmospheres.
 10. The apparatus according to claim 9, wherein said shock wave generator includes a point-source shock wave generator, and said collimator for applying the generated shock waves in a collimated condition to the bone includes a paraboloidal reflector, said point source shock wave generator being located at the focal point of the paraboloidal reflector.
 11. The apparatus according to claim 10, wherein said point-source shock wave generator includes a spark gap.
 12. The apparatus according to claim 9, further comprises a liquid compressional-wave acoustic coupler through which the generated shock waves are coupled to the patient.
 13. The apparatus according to claim 12, further comprising wheels located under the apparatus thereby providing mobility to enable moving said acoustic coupler against the skin of the patient whose bone is to be treated.
 14. The apparatus according to claim 9, wherein said shock wave generator includes an area-source shock wave generator.
 15. The apparatus according to claim 14, wherein said area-source shock wave generator includes an electromagnetic device. 